Connect to Office 365 with different methods

Connect to Office 365 using Global Admin User

Note that only the credentials specified in the Admin account step are used to connect to the source or target server. Credentials provided in the Configuration step are only used once to assign the missing roles. Therefore, you will not be asked to provide the credentials of other admin users again as long as you use the same admin account for the migration process. If you intend to provide the credentials of a Global administrator account that has the multi-factor authentication enabled, make sure to enter the app password instead of the regular Office 365 password. Otherwise, the program will not be able to use this account to assign the missing roles.

Prerequisite:

You need to use Global Admin account for login
Must set impersonation rights to the Global Admin account

Office 365 multiple tenants connection using Admin user and impersonation rights.
In the Office 365 connection wizard to begin the migration process if you want to connect using global admin user then select “ Connect using global admin user” and select the required mail items and click “ next” to move into further step.
Now the login wizard will open in that you need to login with your organizational login credentials to allow you to continue working with migration process
After successful login, below message box will be displayed. If you choose “yes” it will display previously stored mailboxes
If you choose “No” next wizard will open to display list of mailboxes select one of them
Load Mailboxes Automatically
This option lists all the mailboxes for it failed to load then you can easily load using .CSV file.
Load Mailboxes using .CSV file
In this option you have to do the following steps to load mailboxes
Load mailboxes from previously stored list
This option will display all the mailboxes which are stored previously.
Advantage
Using Global Admin Account it lets you to use the single Global Admin account to migrate any Exchange server mailboxes no need to login for each and every users for effective email migration.
If you are using Global Admin then you need to use Global Admin account for login and you must set impersonation rights to the Global Admin account otherwise application does not allow you to access source mailbox and to take everything as planned by the application.

Assign Office 365 global administrator role to a user account

Steps to connect to Office 365 as global admin

Connect to Office 365 using Global Admin User